Osteoporosis is a phenomenon resulting in the weakening of the bones due to the reduction in bone mineral density and changes in the micro architecture of bone due to the depletion of minerals like calcium and bone protein. The evaluation of osteoporosis or the loss of bone minerals and the treatment or prevention of the osteoporosis is performed by usually measuring the bone density.
Some of the devices used for measuring the bone density include X-ray device, gamma ray detector device and ultrasound device, etc. In general, a system used for conducting the bone analysis using the ultrasound, comprises a pair of transducers between which the part of the human body to be analyzed is positioned. One of the two transducers emits ultrasonic waves, while another transducer receives the ultrasonic waves from the human body part under analysis. The elasticity and the density of the bone are measured using the calculated velocity of the ultrasonic signal (SOS) through the bone of a patient. A clear picture of bone density and the micro architecture of cancellous bone are acquired by calculating the broadband ultrasonic attenuations (BUA) in bones. The attenuation of the ultrasound signals with a frequency of 200 KHz-600 KHz, is measured.
A doctoral thesis by Langton entitled “The measurement of broadband ultrasound attenuation in cancerous bone” dated July 1984, explains the measurement of the velocity of sound and broadband ultrasonic attenuation (BUA) through the Os calcis of the heel.
Also, U.S. Pat. No. 5,054,490 discloses a technique to measure the BUA and SOS in bones after immersing the heel of patient in water.
In some conventional bone assessment techniques such as, for example, a QUS technique, for measuring the physical properties of the bone, there are several sources of error and factors that reduce the accuracy and the precision of the measurement result. For example, the assumption of a soft tissue of fixed thickness around the heel during the estimation of ultrasound velocity generates an error in SOS measurement. The precision and the accuracy of the measurement are varied with respect to the variation in thickness of the soft tissue. The thickness of the soft tissue is varied due to the loss or gain of weight or due to the development of the ankle edema. Moreover, the BUA measurement result acquired from the above-mentioned methods is varied with respect to the variation in bone width. Since both the BUA and SOS values are used independently to calculate the bone mineral density (BMD), the accuracy of the measurement of the parameters is not sufficiently high.
An error is also generated in speed of sound (SOS) measurement during the usage of dry coupling pads due to the variation in the quantity of squish in the coupling pad on contact with the heel of subject depending on the shape of the heel of the patient. So the squish in the coupling pads is to be measured accurately instead of assuming a fixed amount of squish compensation.
Moreover, an error in the measurement of SOS Parameters is generated due to the variation in the timing signals like activating time, switching time of ultrasound transducers and time of detection of received ultrasound signal at receiver above a specified threshold due to the limitation of hardware and processing speed. Even a small variation caused due to abovernentioned factors induces unacceptable variation in various diagnostic parameters. Hence there is a need to accurately control the various timing signals.
All the ultrasound based measurement devices using dry coupling pads (gel pads) do not provide sufficient safety from cross infection as the same set of coupling pads is used for several patients. There is also a need for a method to remove the gel pads easily. Hence there is a need to improve the accuracy of bone density measurement and to prevent cross contamination among several patients.